Three-arm knob



1.1 is a rear elevation view of the three-arm knob showing our new design;

1.2 is a front elevation view thereof;

1.3 is a top plan view thereof;

1.4 is a right side elevation view thereof;

1.5 is a left side elevation view thereof; and

1.6 is a bottom view thereof. 

CLAIM The ornamental design for a three-arm knob, as shown and described. 